1. Field of the Invention
The present invention generally relates to layout determination methods, methods of manufacturing semiconductor devices, and computer-readable programs, and more particularly to a layout determination method for determining a layout when producing a semiconductor device by exposing patterns by an electron beam, a method of manufacturing semiconductor devices using such a layout determination method, and a computer-readable program for causing a computer to execute such a layout determination method or method of manufacturing the semiconductor device. The present invention also relates to a computer-readable storage medium which stores such a computer-readable program.
2. Description of the Related Art
[Electron Beam Exposure Apparatus]
In an exposure process of the method of producing the semiconductor device, patterns are transferred on a resist that is coated on a wafer. The electron beam exposure can transfer extremely fine patterns when compared to the exposure using ultraviolet light, and has been developed as the exposure method for the next generation.
FIGS. 1A and 1B are diagrams showing examples of the electron beam exposure apparatus. FIG. 1A shows a case where a variable rectangle exposure is carried out, and FIG. 1B shows a case where a one-shot exposure is carried out.
An electron beam emitted from an electron gun 1 is formed into a square shape having a side of 5 μm, for example, by a first aperture 2. As shown in FIG. 1A, in the case of the variable rectangle exposure which exposes the patterns one pattern at a time, the electron beam that is shaped by the first aperture 2 is shaped into an arbitrary size by a second aperture 3, so as to expose the pattern on a wafer 6.
As shown in FIG. 1B, in the case of the one-shot exposure, a mask (hereinafter referred to as a block mask) 4 which can accommodate a pattern group (hereinafter referred to as a block) for exposing 100 to 400 kinds of patterns in one-shot, for example, is set at the second aperture, so as to irradiate the electron beam that is shaped by the first aperture 2 at a block arranging position 5 of the block mask 4. For example, apertures having the shape of patterns that are enlarged to 25 to 60 times the size of the finally exposed patterns are formed at the block arranging position 5, and the patterns are exposed on the wafer 6 by the electron beam that is shaped by these apertures.
The one-shot exposure requires a smaller number of shots when compared to the variable rectangle exposure, and can therefore improve the throughput of the semiconductor device production. In addition, since it takes approximately 2 weeks to complete the block mask 4 when an order is placed to a mask manufacturer to create the block mask 4, the block mask 4 is not created for each semiconductor device, and a common block mask is create for each technology according to the width (nm) of the transistor gate layer, such as the 95 nm technology and the 65 nm technology. In other words, when using the block mask for the 90 nm technology, for example, the exposure processes of all semiconductor devices are carried out using this block mask as a common block mask. The block mask accommodates blocks of RAMs, ROMs, input and output (I/O) parts and the like.
[Exposure Data Processing]
In the exposure data processing that processes the exposure data used when carrying out the electron beam exposure, design data storing patterns of semiconductor devices are converted into the exposure data. The exposure data stores variable rectangle exposure patterns, blocks and the like. The electron beam exposure apparatus reads the exposure data, and converts the exposure data into a format suited for the exposure. In addition, the exposure data is created for each layer of the semiconductor device to be exposed, such as the wiring layer and the via layer.
[Layout And Exposure Sequence]
FIG. 2 is a diagram showing an example of the layout of the semiconductor devices on the wafer 6. As shown in FIG. 2, a plurality of semiconductor devices 11 are arranged on the wafer 6. Each semiconductor device 11 has a size 12 in an X-direction and a size 13 in a Y-direction.
For example, the layout specification of the semiconductor devices 11 is determined for each wafer size, and one semiconductor devices 11 is arranged by matching its center to a center 14 of the wafer 16, and arranging one column of semiconductor devices 11 along the Y-direction by matching centers thereof to a dotted line 15. Next, columns of semiconductor devices 11 are similarly arranged by matching centers thereof to corresponding dotted lines 16 through 20, on the right side of the center 14 of the wafer 6. In addition, the semiconductor devices 11 are similarly arranged on the left side of the center 14 of the wafer 6. A size 21 in the X-axis direction is a value obtained by adding a size of 50 μm, for example, due to dicing or the like to the size 12 in the X-direction of the semiconductor device 11. Similarly, a size 22 in the Y-axis direction is a value obtained by adding a size of 50 μm, for example, due to dicing or the like to the size 13 in the Y-direction of the semiconductor device 11. If the semiconductor device 11 in its entirety cannot be accommodated within the wafer 5, the semiconductor devices 11 indicated by the hatching in FIG. 2, for example, are not exposed, and the semiconductor devices 11 indicated by the hatching are actually not produced.
FIGS. 3A and 3B are diagrams for explaining the exposure sequence of the semiconductor devices 11. A range (hereinafter referred to as a field) in which the electron beam can be irradiated is set in the electron beam exposure apparatus, and for example, the semiconductor devices 11 are sectioned into fields having sizes 25 as shown in FIG. 3A. The exposure is carried out in a sequence indicated by an arrow 23 in FIG. 3B, from the bottom to top of the field size 25 and from the top to bottom of the field size 25. More particularly, the electron beam exposure apparatus moves a based on which the wafer 6 is placed, so as to carry out the exposure in the sequence indicated by the arrow 23 in FIG. 2. When the exposure folds back (or switches back) along the moving direction, the adjustment of the moving speed and the positioning (or alignment) to carry out the exposure at the correction position are made, and thus, the exposure is not carried out for a predetermined time.
[Wafer Process]
A wafer process refers to the process of creating the semiconductor devices on the wafer 6, and can mainly be categorized into a process of forming transistors (hereinafter referred to as a substrate process) and a process of forming wirings (hereinafter referred to as a wiring process).
More particularly, basic processes such as exposing, developing, etching, cleaning, thermal process, ion implantation, thin film formation, and planarization of interlayer insulator are carried out. For example, a plurality of wiring layers and via layers are formed in the wiring process, and a plurality of basic processes are carried out for each of the wiring layers and via layers. The numbers of wiring layers and via layers respectively are 5 to 8, for example, and there are 10 to 16 wiring layers and via layers in total, for example. Accordingly, the total number of basic processes becomes 100 or greater, for example.
A Japanese Laid-Open Patent Application No. 2005-268611 proposes a method of producing a semiconductor device, in which conditions and evaluation data to be used after a preprocessing of a sample wafer are created before the preprocessing.
For example, when creating semiconductor devices having a width and a height that are both 10 mm on a wafer having a radius of 300 mm, approximately 700 semiconductor devices may be arranged on the wafer. If the number of shots for one wiring layer is 100 M, the number of shots for the entire wafer becomes 70 G, and it takes 12 hours or more for the exposure according to the capability of the existing electron beam exposure apparatus. For this reason, if the time limit of delivery from the time of order of the semiconductor devices, it is difficult to produce the semiconductor devices to meet the time limit of delivery. Normally, before the semiconductor devices are mass produced, semiconductor devices for which the reliability is not guaranteed are forwarded to the customer as engineering samples (ESs), but normally, the time limit of delivery of such engineering samples is relatively short from the time of order.
In addition, if the wafer having the radius of 200 mm is used, the number of semiconductor devices having the same size that may be arranged on the wafer is approximately 300, and the exposure time is approximately 6 hours. But presently, the semiconductor devices subsequent to the 90 nm technology are produced on a production line exclusively for the wafer having the radius of 300 mm, and the wafer having the radius of 200 mm cannot be used on the production line exclusively for the wafer having the radius of 300 mm. In other words, in order to use the wafer having the radius of 200 mm, it is necessary to set up a production line exclusively for the wafer having the radius of 200 mm. Therefore, in the environment in which the production line exclusively for the wafer having the radius of 300 mm is set up, it is impossible to use the wafer having the radius of 200 mm so as to meet the time limit of delivery of the engineering samples, for example.